The
blkid program is the command-line interface to
working with the libblkid(3) library. It can
determine the type of content (e.g. filesystem or swap) that
a block device holds, and also the attributes (tokens,
NAME=value pairs) from the content metadata (e.g. LABEL or
UUID fields).

It is
recommended to use lsblk(8)command to get
information about block devices, or lsblk --fs to get an
overview of filesystems, or findmnt(8)to search in
already mounted filesystems.

lsblk(8)
provides more information, better control on output
formatting, easy to use in scripts and it does not require
root permissions to get actual information. blkid
reads information directly from devices and for non-root
users it returns cached unverified information. blkid
is mostly designed for system services and to test libblkid
functionality.

When
device is specified, tokens from only this device are
displayed. It is possible to specify multiple device
arguments on the command line. If none is given, all devices
which appear in /proc/partitions are shown, if they
are recognized.

blkid
has two main forms of operation: either searching for a
device with a specific NAME=value pair, or displaying
NAME=value pairs for one or more specified devices.

For security
reasons blkid silently ignores all devices where the
probing result is ambivalent (multiple colliding filesystems
are detected). The low-level probing mode (-p)
provides more information and extra return code in this
case. It’s recommended to use wipefs(8) to get
a detailed overview and to erase obsolete stuff (magic
strings) from the device.

The size
and offset arguments may be followed by the
multiplicative suffixes like KiB (=1024), MiB (=1024*1024),
and so on for GiB, TiB, PiB, EiB, ZiB and YiB (the
"iB" is optional, e.g. "K" has the same
meaning as "KiB"), or the suffixes KB (=1000), MB
(=1000*1000), and so on for GB, TB, PB, EB, ZB and YB.
−c, −−cache−filecachefile

Read from cachefile
instead of reading from the default cache file (see the
CONFIGURATION FILE section for more details). If you want to
start with a clean cache (i.e. don’t report devices
previously scanned but not necessarily available at this
time), specify /dev/null.

−d,
−−no−encoding

Don’t encode non-printing
characters. The non-printing characters are encoded by ^ and
M- notation by default. Note that the
−−output udev output format uses a
different encoding which cannot be disabled.

−g,
−−garbage−collect

Perform a garbage collection
pass on the blkid cache to remove devices which no longer
exist.

−h,
−−help

Display a usage message and
exit.

−i,
−−info

Display information about I/O
Limits (aka I/O topology). The ’export’ output
format is automatically enabled. This option can be used
together with the −−probe option.

−k,
−−list−filesystems

List all known filesystems and
RAIDs and exit.

−l,
−−list−one

Look up only one device that
matches the search parameter specified with the
−−match−token option. If there are
multiple devices that match the specified search parameter,
then the device with the highest priority is returned,
and/or the first device found at a given priority. Device
types in order of decreasing priority are: Device Mapper,
EVMS, LVM, MD, and finally regular block devices. If this
option is not specified, blkid will print all of the
devices that match the search parameter.

−L,
−−labellabel

Look up the device that uses
this filesystem label; this is equal to --list-one
--output device --match-token LABEL=label. This
lookup method is able to reliably use /dev/disk/by-label
udev symlinks (dependent on a setting in /etc/blkid.conf).
Avoid using the symlinks directly; it is not reliable to use
the symlinks without verification. The -−label
option works on systems with and without udev.

Unfortunately,
the original blkid(8) from e2fsprogs uses the
-L option as a synonym for -o list. For better
portability, use -l -o device -t LABEL=label
and -o list in your scripts rather than the -L
option.

−n,
−−match−typeslist

Restrict the probing functions
to the specified (comma-separated) list of superblock
types (names). The list items may be prefixed with
"no" to specify the types which should be ignored.
For example:

blkid --probe
--match-types vfat,ext3,ext4 /dev/sda1

probes for
vfat, ext3 and ext4 filesystems, and

blkid --probe
--match-types nominix /dev/sda1

probes for all
supported formats except minix filesystems. This option is
only useful together with −−probe.

−o,
−−outputformat

Use the specified output
format. Note that the order of variables and devices is not
fixed. See also option -s. The format
parameter may be:

full

print all tags (the default)

value

print the value of the tags

list

print the devices in a user-friendly format; this output
format is unsupported for low-level probing
(−−probe or
−−info).

print the device name only; this
output format is always enabled for the
−−label and −−uuid
options

udev

print key="value" pairs for easy import into
the udev environment; the keys are prefixed by ID_FS_ or
ID_PART_ prefixes. The value may be modified to be safe for
udev environment; allowed is plain ASCII, hex-escaping and
valid UTF-8, everything else (including whitespaces) is
replaced with ’_’. The keys with _ENC postfix
use hex-escaping for unsafe chars.

The udev output
returns the ID_FS_AMBIVALENT tag if more superblocks are
detected, and ID_PART_ENTRY_* tags are always returned for
all partitions including empty partitions.

This output
format is DEPRECATED.

export

print key=value pairs for easy
import into the environment; this output format is
automatically enabled when I/O Limits
(−−info option) are requested.

The
non-printing characters are encoded by ^ and M- notation and
all potentially unsafe characters are escaped.

−O,
−−offsetoffset

Probe at the given
offset (only useful with −−probe).
This option can be used together with the
−−info option.

−p,
−−probe

Switch to low-level superblock
probing mode (bypassing the cache).

Note that
low-level probing also returns information about partition
table type (PTTYPE tag) and partitions (PART_ENTRY_* tags).
The tag names produced by low-level probing are based on
names used internally by libblkid and it may be different
than when executed without −−probe (for
example PART_ENTRY_UUID= vs PARTUUID=).

−s,
−−match−tagtag

For each (specified) device,
show only the tags that match tag. It is possible to
specify multiple −−match−tag
options. If no tag is specified, then all tokens are shown
for all (specified) devices. In order to just refresh the
cache without showing any tokens, use
−−match−tag none with no other
options.

−S,
−−sizesize

Override the size of
device/file (only useful with
−−probe).

−t,
−−match−tokenNAME=value

Search for block devices with
tokens named NAME that have the value value,
and display any devices which are found. Common values for
NAME include TYPE, LABEL, and
UUID. If there are no devices specified on the
command line, all block devices will be searched; otherwise
only the specified devices are searched.

−u,
−−usageslist

Restrict the probing functions
to the specified (comma-separated) list of
"usage" types. Supported usage types are:
filesystem, raid, crypto and other. The list items may be
prefixed with "no" to specify the usage types
which should be ignored. For example:

blkid --probe
--usages filesystem,other /dev/sda1

probes for all
filesystem and other (e.g. swap) formats, and

blkid --probe
--usages noraid /dev/sda1

probes for all
supported formats except RAIDs. This option is only useful
together with −−probe.

−U,
−−uuiduuid

Look up the device that uses
this filesystem uuid. For more details see the
−−label option.

If the
specified device or device addressed by specified token
(option −−match−token) was found
and it’s possible to gather any information about the
device, an exit code 0 is returned. Note the option
−−match−tag filters output tags,
but it does not affect return code.

If the
specified token was not found, or no (specified) devices
could be identified, an exit code of 2 is returned.

For usage or
other errors, an exit code of 4 is returned.

If an
ambivalent probing result was detected by low-level probing
mode (−p), an exit code of 8 is returned.

The standard
location of the /etc/blkid.conf config file can be
overridden by the environment variable BLKID_CONF. The
following options control the libblkid library:
SEND_UEVENT=<yes|not>

Sends uevent when
/dev/disk/by-{label,uuid,partuuid,partlabel}/ symlink
does not match with LABEL, UUID, PARTUUID or PARTLABEL on
the device. Default is "yes".

CACHE_FILE=<path>

Overrides the standard location
of the cache file. This setting can be overridden by the
environment variable BLKID_FILE. Default is
/run/blkid/blkid.tab, or /etc/blkid.tab on
systems without a /run directory.

EVALUATE=<methods>

Defines LABEL and UUID
evaluation method(s). Currently, the libblkid library
supports the "udev" and "scan" methods.
More than one method may be specified in a comma-separated
list. Default is "udev,scan". The "udev"
method uses udev /dev/disk/by-* symlinks and the
"scan" method scans all block devices from the
/proc/partitions file.